# Geometry and mesh / with compressible air area

## Introduction

This paragraph deals with rotation or translation motion of a moving part in a compressible air area.

## Technique used

The technique used consists in dissociating the different parts and re-meshing only the compressible part ; the fixed and moving parts are not re-meshed.

This technique is detailed in the following blocks.

## Dissociation surfaces

The dissociation surfaces are the surfaces situated between the volumes belonging to:

• the fixed mechanical set and the compressible area
• the mobile mechanical set and the compressible area

## Separation of objects

To re-mesh the compressible area of air, independently of moving and fixed parts, a separation of geometrical objects (points, lines and faces) and of mesh objects (nodes, line elements and surface elements) is made at the level of the dissociation surfaces.

The mechanical sets become entirely independent from the geometric and meshing points of view.

In this situation, a non-conforming mesh is authorized at the level of the dissociation surface.

## “Mesh connection” technique

The technique of “mesh connection” on the two sides of the dissociation surface consists of an interpolation of nodal values of the surface elements.

Each nodal value on each node of a surface element situated on one side is expressed as a linear function of the nodal values of the neighboring surface elements on the other side. This is done in order to ensure the continuity of state variable.